(a) Technical Field of the Invention
The present invention is related to a light guide plate (LGP) and LGP-based flat fluorescent panel (FFP), and more particularly, to one that upgrades the general light emitting efficacy of the FFP by eliminating the light interference of light and shade stripes.
(b) Description of the Prior Art
Whereas the liquid crystal penal adapted in an LCD is not capable of emitting light, a flat fluorescent panel (FFP) is required to provide a light source for achieving the purpose of display.
As illustrated in FIG. 1, an FFP 1 of the prior art is essentially comprised of a light guide plate 11, one or multiple diffuser 12 and condenser 13 are disposed in sequence on the light outlet surface 111 of the light guide plate 11; multiple light guide points 113 in great number are provided on the reflective surface of the light guide plate 11; a reflector 14 is adhered to the outer side; one light inlet surface 114 as a minimum is provided on the light guide plate 11; a lamp source 15 is adapted externally to the light inlet surface 114; and the lamp source is substantially covered up by a lamp reflector 16.
In operation of the prior art as illustrated in FIG. 2, the light source from the lamp source 15 forthwith emits into the light inlet surface 114 of the light guide plate 11 due to the reflection by the lamp reflector 16. Upon entering into the interior of the light guide plate 11 by the light source, if the angle formed by the route of the light source and the light outlet 111 of the light guide plate 11 is smaller than the critical angle, the light source leaves the light guide plate 11 and varied through the diffuser 12 to achieve the purpose of condensing through the condenser 13 and finally the light source inputs toward a liquid crystal panel 2 to provide sufficient light source when the liquid crystal panel displays. Should the angle indicated by the light source in the light guide plate 11 and the light outlet surface 111 of the light guide plate 11 be greater than the critical angle, the light source indicates reflection to a reflective surface 112 to further take advantage of those light guide points 113 and the reflector 14 for reflecting its light source in seeking for the chance to output the light once again.
However, the FFP 1 of the prior art is vulnerable to the following flaws. As illustrated in FIG. 3, since the light inlet surface of the light guide plate 11 relates to a mirror without having been fogged and roughened; the incident angle is comparatively smaller when the light source from the lamp source 15 enters into the light guide plate 11. The light source arrives in the vicinity of the edge of the light outlet surface abutted to the light inlet surface 114 is prevented from leaving the light outlet surface 111 due to that the incident angle of the light source is greater than the critical angle resulting in reflection. The light guide source after the primary reflection undergoes the second reflection through those light guide points 113 and the reflector 112. Whereas the incident angle is equal to the exit angle, when the light source of the second reflection reaches once again on the light outlet surface 111, the angle indicated by the light source of the second reflection and the light outlet surface 111 is greater than the critical angle to frustrate the deflection. The repeated pattern creates the light interference to indicate light and shade stripes on the light guide plate 11, resulting in inconsistent luminance of the entire FFP and reduced total luminance to become problems pending urgent solutions by the trade.
To improve, an FFP 3 as illustrated in FIG. 4 contains a light guide plate 31; one or multiple diffuser 32 and condenser 33 in sequence on the light outlet surface 311 of the light guide plate 31; multiple light guide points 313 in great number on the reflective surface 312 of the light guide plate 31 and then covered up with a reflector 34. Meanwhile, one light inlet surface 314 as a minimum is provided on the light guide plate 31. The light inlet surface 315 is not mirrored, instead, is molded, sandblasted, etched, or tooled into fogged or roughened status. A lamp source 35 is provided to the light inlet surface 314 and is substantially covered up by a lamp reflector 36.
As the light inlet surface 314 of the light guide plate 31 is in fogged or roughened status, the angle of the light source form the lamp source 35 is expanded upon entering into the light inlet surface 314 of the light guide plate 31. Accordingly, the angle of the primary light source in the vicinity of the edge of the light outlet surface 311 abutted to the light inlet surface is smaller than the critical angle for the light outlet surface 311 to successfully become a bright area.
However, as illustrated in FIG. 5, the angle of a primary light source L1 farther from the light inlet surface 414 is gradually becoming equal to and larger than the critical angle to frustrate the light outlet and to turn into a dark area due to reflection even though the delivery of the light by the light source in the vicinity of the edge of the light inlet surface 314 abutted to the light outlet surface 311 presents no problem. The light source of that reflection is a secondary light source L2 and it though may be further reflected by those light guide points 313 and the reflector 34, the second reflection by the secondary light source L2 becomes the tertiary light source L3 due to that the incident angle of the light source is equal to the exit angle; and the attempted emission through the light outlet surface 311 by the tertiary light source L3 is frustrated since the light source is prone to be greater than the critical angle, thus is reflected again, and so on. As a result, the light interference exists to create light and shade stripes, the luminance of the FFP 3 is still not consistent, and the total luminance is insufficient with the problems found with the prior art not solved.
While the liquid crystal display is heading for larger and for full color display, more demands are put on the luminous of the FFP to point the way for future efforts by the trade. More recently, a high luminance FFP has been developed as illustrated in FIG. 6. Wherein, a light guide plate 41 is provided to an FFP 4, and the light guide plate 41 is provided with a light outlet surface 411 and a reflective surface 412. Multiple channels 413 in V shape capable of collecting the light and one light inlet surface 414 as a minimum are provided to the reflective surface. A reflector 42 is adhered to the reflective surface 412. A lamp source 43 is provided externally to the light inlet surface 414, and is substantially covered up by a lamp reflector 44. The light outlet surface is adhered with a condenser 45. As illustrated in FIG. 7, both of the light outlet surface 411 and the light inlet surface 414 of the light guide plate 41 in the FFP 4 are fogged or roughened to provide soft and consistent light outlet by the subsequent light outlet from the light guide plate 41 by omitting the installation of the conventional diffuser to save the material cost and assembly cost of the diffuser for condensing the light directly through the condenser 45 to concentrate the visual angle of luminance and significantly upgrade the luminance of the FFP 4.
However, the omission of the diffuser and the even further concentration of the visual angle of luminance lead to the even more conspicuous of the light and shade stripes on the light outlet surface, presenting a problem pending urgent solution for the FFP 4. Referring to FIG. 8, light beams from the light inlet surface partially advance in parallel for transmission into the light guide plate 41, and the remaining light beams are generally transmitted to the light outlet surface (411) upwardly and to the reflective surface (412) downwardly. For those light beams transmitted upwardly, their light emission angle has been already expanded by the fogged or roughened light inlet surface 414, the light angle of the primary light source L1 falling in the vicinity of the edge of the light outlet surface 411 abutted to the light inlet surface 414 is smaller than the critical angle and the light is smoothly deflected for the area of the primary light source L1 to become a bright area. As the location of the primary light source L1 falling on the light outlet surface 411 moves farther from the light inlet surface 414, the angle of the primary light source L1 and the critical angle of the light outlet surface 411 become larger until the deflection is prevented due to that the light angle of the primary light source L1 is greater than the critical angle. Accordingly, a dark area B is crated on the light outlet surface 411 and the light is reflected to the reflective surface 412 to become a secondary light source L2. Where as the incident angle is always equal to the reflective angle, the secondary light source is reflected once again to the light outlet surface 411 to become a tertiary light source L3. When the tertiary light source L3 is reflected once again to the light outlet surface by following the rule that the incident angle is always equal to the reflective angle, the light angle is greater than the critical angle to become a dark area, and so on. Consequently, the light and shade stripes are created to bring in the subsequent transmission of light the poor deviation to the highly luminance demanding FFP 4.